The present invention is drawn to a check valve and, more particularly, a multiple component plug check valve employed in a pumping unit for pumping crudes and the like wherein the check valve has a specific design which guarantees minimum pressure drop across the valve and thus maximum flow through the valve body.
In the petroleum industry, positive displacement pumps are used in numerous applications including the pumping of crudes from subsurface wells. Typical positive displacement pumps used in the petroleum industry employ intake and discharge valves which are typically check valves which comprise a valve seat onto which a ball rests and seals against the valve seat. A typical positive displacement pump is disclosed, for example, in U.S. Pat. No. 4,018,547.
The typical check valve configuration is very efficient when pumping liquids. However, it has been found that if a reciprocating positive displacement pump is used to pump a two-phase mixture, that is, a gas-liquid mixture, the pumping efficiency rapidly decreases as the gas content of the two-phase mixture increases. It is quite common in the petroleum industry when pumping crudes from subsurface wells to have a gas entrained in the crude. In order to maximize pumping efficiency when pumping a two-phase mixture with a reciprocating positive displacement pump, it has been found that typical check valves as discussed above are unsatisfactory. In order to increase pumping efficiency, it has been found that the valves employed should offer a minimum restriction to flow through them as a large restriction would produce an increase in pressure drop across the valves which in turn causes part of the liquid phase of the two-phase mixture being pumped to flash into the gaseous phase thereby resulting in a decrease in efficiency of the pumping operation. This phenomena occurs when employing downhole reciprocating pumps to extract oil from underground reservoirs. In addition, a critical condition known as gas lock is a common occurrence in oil field operations and the origin of this phenomena has been traced to excessive pressure drop which occurs across the typical intake valves of the reciprocating pumps. Gas lock is a phenomena wherein the mechanical work done by the subsurface pump is used to compress and expand large gas bubbles trapped inside the pump without any pumping of the crude oil being effected. A similar critical condition known as steam lock occurs when steam has been injected downhole into wells in order to stimulate crude recovery.
Naturally, it would be highly desirable to provide an improved check valve construction which would minimize pressure drop across the intake and discharge valves of a positive displacement pump and thereby maximize flow through the valve body resulting in improved pumping efficiency while eliminating gas lock, steam lock and other disadvantages noted above with respect to typical check valves presently employed in the art.
Accordingly, it is the principal object of the present invention to provide a check valve wherein the pressure drop across the check valve is minimized so as to insure maximum flow through the check valve.
It is a particular object of the present invention to provide a check valve as aforesaid which is a multi-component plug check valve.
It is a further object of the present invention to provide a check valve as aforesaid which is of relatively simple construction and inexpensive to manufacture.
Further objects and advantages of the present invention will appear hereinbelow.